It is known in the art to use built in electronic correction circuits with sensors that measure pressure, temperature, and other physical quantities so as to make the sensor output more linear and proportional to the measured quantity. Such correction circuits are needed because the output of sensors may vary from ideal by ten percent or more.
One prior art correction technique uses analog compensation of the output voltage with elaborate networks of resistors and amplifiers. But the compensating components must be very stable and are thus expensive. In addition, a great deal of expensive manufacturing labor is consumed to measure the errors, calculate the size and value of the compensating components, and verify the proper correction of the errors after the installation of the correcting components. The process usually must be repeated several times to reduce the error even below 2 percent of full scale output. Finally, it is entirely possible that component value drift over time may increase the output error again. So this method is very unsatisfactory.
Another prior art technique uses digital correction which can be as accurate as desired, and more stable, but is very expensive. This method uses a large look up table, in a suitable memory, which maps all of the sensor errors for the range of possible outputs and for all other variables that could affect output, such as temperature. This method is less complex than analog designs. But the manufacturing time needed to gather all the data for the table makes this approach expensive. Furthermore, in order to achieve higher accuracies, very large memories are needed to hold the table. Also, it is impractical to recalibrate the sensor in the field for large tables which could easily contain as many as 32 thousand bytes. The present invention avoids these problems with an accurate digital approach that does not have massive memory requirements.